Plant biostimulants, biopesticides and other biologicals

Numerous biological products claim to benefit your crops. With the range of biostimulants and biopesticides increasing, we examine the key product types, how they are regulated and whether they work.

There is a wide range of products marketed as ‘biologicals’ in the UK.

Our evidence-based guidance won’t tell which products to buy, but it will give you the knowledge and confidence to decide whether, when and where a biological has a place on your farm.

There is no regulatory definition of biologicals.

The term covers approaches based on living organisms or substances derived from living organisms that influence crops, nutrition, soils, pests or diseases.

It may also cover other naturally occurring substances.

Biological products are associated with a wide variety of ingredients and functions.

The evidence to support marketing claims and regulatory status is also variable.

In practice, it is important to focus on the potential agronomic benefits, rather than a product’s ingredients.

Our web-based guidance explores two key groups of products: biostimulants and biopesticides.

A biostimulant contains substances or microorganisms that stimulate natural plant processes.

Biostimulants are marketed with a range of potential benefits to the plant or the plant root zone/rhizosphere:

• Nutrient-use efficiency, by improving nutrient uptake or availability
• Tolerance to environmental stress, such as drought
• Supported crop quality
• Availability of nutrients in the soil or rhizosphere

Any effect should be independent of its nutrient content.

Additionally, biostimulants should not have pesticidal activity, unless authorised for use as a plant protection product.

Biostimulant product regulation is still in its infancy. 

In the UK, a diverse range of biostimulants is available commercially.

These are either ‘microbial’ or ‘non-microbial’ and can be further classified by product type.

Note: The above page does not cover farm-made preparations, such as Johnson–Su-style compost extracts, other home-made microbial inoculants or compost teas.

Management needs to adapt to the biostimulant in question.

As microbial biostimulants contain living organisms, they require particularly careful management before, during and after application.

AHDB has reviewed the evidence on the efficacy of biostimulants used on cereal and oilseed rape crops.

A biopesticide is a plant protection product based on a biological agent or substance of biological origin that can have biofungicidal, bioinsecticidal or bioherbicidal activity.

The horticulture sector has often driven innovation in biopesticides, due to particularly pressing crop protection challenges and the relatively high-value nature of many horticultural commodities.

Discover the main biofungicide types and how they have been classified into several mode of action groups by the Fungicide Resistance Action Committee (FRAC), as well as the key considerations when using them in crop protection programmes.

Learn about the main bioinsecticide types, including their classification into mode of action groups by the Insecticide Resistance Action Committee (IRAC), as well as the key considerations on how to use them, when they come to market.

The bioherbicide development rate is much slower, compared to biofungicides and biopesticides.

Globally, various natural substances have been identified that can cause injury to plants, but commercial products are extremely limited.

Pelargonic acid is an example of a plant-derived substance for general weed control, which is authorised for use in limited situations in the UK. Its mode of action is unknown.

We are watching developments and will develop usage guidance, should products more relevant to cereals and oilseeds come to market.

Baffled by biologicals, such as biostimulants and biopesticides?

This autumn and winter, 2026 to 2027, join farmers, AHDB, the Voluntary Initiative and ADAS experts to explore the science, evidence and practical considerations associated with using biologicals in commercial cereal and oilseed systems.

Our roadshow, which will see 11 in-person events take place across the UK, will explore where biologicals can realistically deliver and where the evidence is still limited or uncertain.

It won’t tell which products to buy, but it will give you the knowledge and confidence to decide whether, when and where a biological has a place on your farm.